1. Field of the Invention
This invention relates to a method of attaching a float stopper in a liquid level sensor. The liquid level sensor to which the present invention appertains is of the type which comprises a switch case made of a thermoplastic synthetic resin and so disposed in a tank as to extend in the vertical direction, a switch, actuated by a magnetic force, disposed within the switch case, a float so fit on the outside of the switch case as to be freely slidable in the vertical direction, a permanent magnet attached to the float, and the float stopper which is attached to the free end of the switch case for limiting the upward or downward stroke of the float.
2. Description of the Prior Art
According to the conventional method of attaching the float stopper, the float stopper is attached to the free end of the thermoplastic switch case by fitting the float stopper, provided beforehand with a central hole, over the outside of a solid, column-shaped caulking projection formed on the free end of the switch case, and applying a high temperature to the tip of the caulking projection by means of a heated caulking tool to melt its surface into a mass which overflows onto the float stopper to form a portion which, upon hardening, locks the float stopper securely in place. With the conventional method, however, the hardened locking portion extending from the caulking projection to the float stopper has poor mechanical strength owing to carbonization and entrapped air bubbles, both of which are the result of melting the projection at high temperature. When the vertically slidable float impacts against the stationary locking portion, therefore, the latter has a tendency to break off of the switch case, permitting the float to drop off the switch case so that the performance of the sensor is impaired.